The present invention relates to a hermetic dynamic machine.
Japanese Utility Model Laid-Open No. 55-78825 discloses a hermetic dynamic machine having an external cooling fan which is composed of two fan blade systems: one for cooling the machine body and the other for bearings. When compared with earlier proposals, this arrangement suffers from problems such as increased mechanical loss, reduced efficiency of the machine, complicated construction of the cooling fan and increased size and cost of the whole machine, due to the additional provision of the fan blade system specifically intended for cooling the bearings.
More specifically, referring to FIG. 4, the hermetic dynamic machine disclosed in Japanese Utility Model Laid-Open No. 55-78825 has a rotor shaft 104 which is provided on the top end thereof with an external fan 106. The rotor shaft 104 also carries a dynamic machine part 102 which is provided with a cooler 108. The end of the dynamic machine with the external fan 106 is covered by an end cover 110 which is provided with a cooling air inlet 118. The end of the rotor shaft 104 adjacent to the external fan 106 is supported by a bearing 128 which is housed in a bearing box 130. The external fan 106 is provided with blades which are composed of main part cooling blades 106a and bearing cooling blades 106b. In operation, cooling air is induced from the air inlet 118 by the suction force produced by the main part cooling blades 106a of the external fan 106. The thus induced cooling air is made to flow through a main part cooling air passage 142 and then through the cooler 108 so as to effectively cool the main part 102 of the hermetic dynamic machine. A part of the air flowing through the main part cooling air passage 142 exits therefrom into a bearing cooling air passage 140 which is provided at the inlet end thereof with a flow-rate adjusting damper 148, by the suction force produced by the bearing cooling blades 106b. This air flows along the bearing box 130 so as to effectively cool the bearing 128 in the bearing box 130.
As stated before, no consideration has been given in this arrangement for obviating various shortcomings attributable to the increase in the size of the external fan 106 and the increase in the mechanical loss. Namely, the cost of the external fan is raised because of the complicated construction and increased size of the external fan, which leads to a rise in the cost and an increase in the size of the whole machine, as well as decreased efficiency of the same.